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Reproductive System > Gametogenesis > Flashcards

Gametogenesis Flashcards

1
Q

Compare the production pattern of gametes in males and females

A

Females: Oogenesis

  • Intermittent production of 400 ova in a lifetime
  • Present from birth, stimulated at puberty

Males: Spermatogenesis
- 200 million sperm made a day, continuously

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2
Q

What do the Primordial Germ Cells do after colonising the Gonad

A
  • Proliferate by mitosis
  • Reshuffle genetically and reduce to Haploid cells by Meiosis
  • Differentiate into mature gametes
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3
Q

Where does Spermatogenesis occur?

A

In Seminiferous tubule walls of testes

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4
Q

Compare Spermatogenesis and Spermiogenesis

A

Spermatogenesis- Results in spermatids being made

Spermiogenesis- Results in Spermatozoa/ mature sperm developing from spermatids

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5
Q

What do the Sertoli cells do?

A

Nurture the developing spermatids

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6
Q

What are the 2 compartments of the seminiferous tubules

What is the junction formed by? What is it called?

A
  • Basal
  • Adluminal

Created by tight junctions between cells, forming the Blood testis/ Sertoli cell barrier

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7
Q

What are 2 functions of the Blood testis barrier?

A
  • Prevent recognition of developing sperm as non self by the immune system
  • Maintenance of 2 separate environments
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8
Q

Describe the process of Spermatogenesis

A
  • In the Basal Compartment, Spermatogonia (germ cells) between Sertoli cells divide by mitosis into 2 Primary Spermatocytes
  • One PS replaces the Spermatogonia, the other one undergoes Meiosis I to produce 2 Secondary Spermatocytes
  • Each SS undergoes Meiosis II to produce 2 Spermatids

(Thus 1 Spermatogonia turns into 4 spermatids)

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9
Q

Spermatids are at different levels of maturation at different sections of seminiferous tubules

Compare the Spermatogenic Cycle and Wave

A

Spermatogenic Cycle: Time taken for (next set of) spermatids at same stage to re-appear at a given point in the cycle

Spermatogenic Wave: Distance between spermatids at same stage of maturation process

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10
Q

How long is the Spermatogenic cycle?

A

16 days

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11
Q

When does Spermiogenesis begin?

How do they change in this process?

A
  • Begins when Spermiation occurs (release of spermatids into seminiferous tubule lumen)
  • Non motile spermatids become motile spermatozoa
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12
Q

Spermiogenesis has finished once the spermatids reach what point in testes?

How are the non-motile spermatids transported to here

A
  • Completed once they reach Epididymis

- Transported via Sertoli cell secretions and assistance by peristaltic contractions

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13
Q

What are the functions of the head and tail of the mature spermatozoa?

A

Head- Contains nucleus

Tail- Provides motility, with mitochondria producing ATP to drive flagella (Muscle used is Dynein not myosin and fructose is used rather than glucose)

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14
Q

What does the Acrosome layer around Head of Sperm allow?

A

Allows sperm to fuse with ovum

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15
Q

Name and describe the final step in sperm become in fertile

A

Sperm capacitation;

  • Occurs in female reproductive tract
  • Removal of Cholesterol and Glycoproteins from outer membrane of sperm
  • This allows sperm to bind to Zona Pellucida of oocyte and initiate the Acrosome Reaction

(Involves activation of sperm signalling pathways, using atypical soluble Adenylyl Cyclase and PKA)

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16
Q

Why is Sperm Capacitation important for IVF?

A

Human sperm must first be incubated in Capacation Media, to induce fertilisation of sperm

17
Q

Describe Oogenesis up to the end of Month 3

3 steps

A
  1. Germ cells settle in ovary to form Oogonia
  2. Some Oognia divide by mitosis, then enter Meiosis and stop at Prophase I, to become Primary Oocytes (stay in Prophase I until puberty)
  3. By end of Month 3, Oogonia and Primary Oocytes are surrounded by Flat Epithelial cells
18
Q

What happens to the Oogonia and Primary Oocytes surrounded by Flat Epithelial Cells before birth?

(3 steps)

A
  • Atresia (degenerative process) begins reducing number of Oogonia and Primary Oocytes
  • By month 7, all remaining Prophase I Primary Oocytes are surrounded by Follicular Cells (used to be flat epithelial)
  • Structure is now called Primordial Follicle (Not including follicular cells)
19
Q

From puberty onwards, how many Oocytes mature each month?

Through what 3 phases do they mature?

A

15-20

  • Preantral
  • Antral
  • Preovulatory
20
Q

Describe the Preantral Phase

3 steps

A
  • Follicular cells surrounding the Primordial Follicle develop and proliferate into a stratified cuboidal epithelium of Granulosa cells
  • Granulosa cells secrete a glycoprotein called the Zona Pellucida
  • It is now called a Primary Follicle

(Thus: Primordial-> Primary follicle)

21
Q

Describe the Antral Phase

4 steps

A
  • Fluid filled spaces appear between Granulosa cells and coalesce to form the Antrum (fluid filled)
  • Granulosa cells surrounding the primary oocyte are now called Cumulus Oophorus cells
  • An outer fibrous layer develops into Theca Interna and Theca Externa
  • Primary follicle is now called a Secondary Follicle
22
Q

Describe the function of the Theca Interna

A
  • Stimulated by LH to produce Androgens

- Androgens converted to Oestrogen by Follicular/ Granulosa cells

23
Q

Describe the Preovulatory phase up to beginning of Meiosis II

(4 steps)

A
  • Phase induced by surge in LH, Secondary follicle completes Meiosis I-> 2 haploid cells
  • Most of cytoplasm goes to 1 daughter cell, the Secondary Oocyte).
  • The other cells is the 1st Polar body and gets very little cytoplasm
  • The follicle enters Meiosis II just before Ovulation, but doesn’t complete it until fertilisation
24
Q

In the Preovulatory phase, many follicles start to develop but only 1 matures fully.

What is this special follicle called?

A

The Graafian follicle

25
Q

If fertilisation does not occur, what happens to the Secondary Oocyte produced in the Preovulatory Phase?

A

Secondary oocyte will degrade 24hrs after ovulation

26
Q

If fertilisation does occur, what happens to the Secondary Oocyte produced in the Preovulatory Phase?

A

A 2nd Polar Body is produced and discarded (all energy is focused on a single ovum at end of this process

27
Q

Describe how the ovum is released from the ovary

A
  • LH surge increases activity of Collagenase
  • Prostaglandins increase response to LH and cause local muscular contractions in ovarian wall
  • Oocyte extruded and released from ovary
28
Q

After ovulation, how is the Corpeus Luteum made and what does it do?

A
  • Granulosa and Theca Interna cells become vascularised, forming Corpus Luteum
  • CL secretes Oestrogen and Progesterone, stimulating uterus to prepare for implantation of an embryo
29
Q

Compare outcomes of fertilisation and no fertilisation after ovulation

A
  • Without fertilisation, CL degenerates after 14 days, forming Corpeus Albicans (a mass of scar tissue) and reduced progesterone production-> Menstrual bleeding
  • With fertilisation, Implanted embryo releases Human Chorionic Gonadotrophin (Beta-HCG)
  • HCG maintains CL (grows into CL Gravidatis) until Placenta can take over Progesterone production

Reproductive System (21 decks)

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